This invention relates to a process for the extruding peroxide crosslinkable polymer parts, mainly tubes, in which the crosslinkable polymer is heated in an extruder and is fed continuously to an extrusion die to create the part and in which at least a partial crosslinking of the polymer occurs in the extrusion die by the heating of the polymer above a crosslinking temperature.
EP 0 999 030A1. describes a process, in which tubes are made of a peroxide crosslinkable polymer. These tubes consist of a polyethylene to which an organic peroxide is added as the crosslinking agent as well as an antioxidant. Other polyolefins, such as polypropylene and copolymers of ethylene and propylene with monounsaturated or poly unsaturated polymerizable monomers can also be used in place of polyethylene. In the process described in EP 0 999 030, the unmolten mixture of the polymer and the peroxide is fed to the extruder through a known feed hopper. The extruder conveys the polymer to the extrusion die, in which the tube is then created and the crosslinking of the polymer is achieved. For this purpose, heat is induced in the vicinity of the extrusion die, which initiates the crosslinking of the polymer. Firstly, the polymer is melted with the crosslinking agent in the extrusion die, and then heated above the crosslinking temperature. The material crosslinked in the extrusion die then discharges from the extrusion die as an extruded tube. To prevent premature melting and crosslinking of the polymer, the extruder is particularly short, in length, and is also equipped with a cooling unit at its exterior.
The finished tubes are particularly suitable as water pipes. Compliance with the process parameters poses a problem in the manufacture of this type of tubes. Failure to address these problems can lead to heavy fluctuations in the quality during the manufacture of the tubes or parts.
Unintended crosslinking can also lead to undesired stresses and loads in the extruder or the extrusion die. Apart from inadequate properties of the finished tube, this can also cause damage to the extrusion die or the extruder.